Many human premature infants develop bronchopulmonary dysplasia (BPD), and some studies suggest a relationship between retinol levels and the incidence or severity of BPD. The overall objective is to clarify the role of vitamin A in the pathogenesis and repair of BPD. First, we will assess the vitamin A (retinol) status of premature infants with an intramuscular Relative Dose Response (IM-RDR) test. Second, we will study how vitamin A relates to BPD and lung on a biochemical level.